Towards a better understanding of the oxygen isotope signature of 18 atmospheric CO2: Determining the O-exchange between CO2 and H2O in leaves and soil on-line with laser-based spectroscopy Laura Gangi*, Youri Rothfuss, Harry Vereecken, Nicolas Brüggemann
WHY
Agrosphere Institute (IBG-3), Forschungszentrum Jülich GmbH, Jülich, Germany
18 δ O-CO2?
CO18O
The oxygen isotope signature of carbon dioxide (δ18O-CO2) is a powerful tool to disentangle CO2 fluxes in terrestrial ecosystems, as CO2 attains a contrasting
18O
on the CO2–H2O isotopic exchange in soils and leaves. • Our approach: Combined on-line monitoring of the δ18O in CO2 and
signature by the equilibration with isotopically different soil and leaf water pools
water vapor during gas exchange in plant leaves and soil with
during soil respiration and photosynthesis, respectively. However, there is still a lack
laser-based spectroscopy (Picarro L2120-i, Campbell TGA200) using
of knowledge concerning the influence of plant/soil type and environmental conditions
plant chambers and soil columns.
CO18O
gs_CO2, δ18O-H2Oev,
CO18O
Figure 3. Relative changes in isoforcing in response to reduced light intensity (3x 30 min 100 µmol phot m-2 s-1 denoted by grey bars).
... is driven by gs, θ, and δ18O-H2Oev to a varying extent depending on the plant species
Figure 1 and 2 (a) Stomatal conductance to CO2 (gs_CO2) and photosynthetically active radiation (PAR); (b) CO18O isoforcing (CO18O-Iso) and leaf δ18O-H2O at evaporation site (δ18O-H2Oev); (c) degree of leaf isotopic H2O–CO2 exchange (θ) and soil water potential (Ψ) in response to decreasing water availability for winter wheat (left) and maize (right).
... decreased at elevated air temperature in all specieexcept maize
... decreased at reduced light intensity in maize and spruce
... decreased with limited water availability
PLANTS´ IMPACT ON AMBIENT CO18O (CO18O isoforcing) ... SUMMARY OF
1 RESULTS
• together stomatal conductance (gs), degree of isotopic CO2-H2O equilibrium (θ), and leaf water δ18O accounted for up to 95 % in the variations in CO18O isoforcing • effect of θ on CO18O only significant for broad-leaved C3 species • effect of stomatal conductance on CO18O isoforcing could become Figure 5. CO18O isoforcing vs. gs_CO2, θ, δ18O-H2Oev for 3 replicates of each plant species. The lines show results from least squares regression (R2 > 0.5 and p < 0.001).
increasingly relevant in a future climate (rising CO2 level)
OUTLOOK • model CO18O fluxes in terrestrial ecosystems with MuSICA 2 • measure δ18O-CO2 and δ18O-H2O (infered from soil water vapor measurements3) and degree of 18O-exchange in soils using gas-permeable tubing and laser-based analyzers
δ18O-H2Oev,
CO18O
Figure 4. Relative changes in isoforcing, gs_CO2, and θ in response to elevated Tair for poplar (P), maize (M), spruce (S), and wheat (W).
REFERENCES
CONTACT INFORMATION
1 Gangi et al., submitted to JGR Biogeosciences (11/2013) 2 Ogee et al. (2004) Global Biogeochemical Cycles 18(2) 3 Rothfuss et al. (2013) Water Resources Research 49(6)
[email protected] http://www.fz-juelich.de/ibg/ibg-3/